1. Field of the Invention
The present invention generally relates to, and more particularly to multi-level (or multi-valued) data processing methods and apparatuses, and more particularly to a multi-level data processing method and a multi-level data processing method which are used when recording and/or reproducing the multi-level data on and/or from an information recording medium such as an optical disk.
2. Description of the Related Art
Conventionally, there was a multi-level data processing method which records on an information recording medium a test data made up of all combinations of a plurality of (3) consecutive multi-level data, creates a table that stores reproduced signal values of the test data at the time of reproducing the multi-level data, and outputs as the reproduced multi-level data the multi-level data which are reproduced and have a smallest error with respect to the reproduced signal values stored in the table.
In addition, when using the table to judge the reproduced multi-level data, there was a multi-level data processing method which judges the first and third multi-level data of the 3 consecutive multi-level data by comparison with a fixed threshold value, and thereafter outputs as the reproduced multi-level data the multi-level data which are reproduced and minimize the error between the second multi-level data and the reproduced signal value stored in the table. In this case, the accuracy of judging the reproduced multi-level data is improved, and the table can be made compact.
Moreover, there was a multi-level data processing method which treats the plurality of multi-level data as one set of multi-level data. The binary data is arranged as it is in the upper bits of each multi-level data, and a data according to a predetermined conversion rule is arranged in a lower one bit so as to convert the binary (bi-level) data into the multi-level data. Since an error is easily generated in the lower one bit when reproducing the multi-level data, the multi-level data is judged by utilizing the fact that the data is in accordance with the predetermined conversion rule. When recording (or transmitting) the multi-level data amounting to n (n≧2) bits/symbol, this multi-level data processing method regards m (m≧2) symbols as 1 set, and arranges an arbitrary binary data in upper {(n−1 bits)×(m symbols)}={(n−1)×m} bits of each symbol, and arranges a binary data which is obtained by converting (m−1) bits into m bits according to the predetermined conversion rule in lower {(1 bit)×(m symbols)}=m bits of each symbol. Although a 1-bit redundant data is generated by the predetermined conversion rule, it is possible to improve the accuracy of judging the multi-level data.
Furthermore, according to this multi-level data processing method, the data obtained by the conversion according to the predetermined conversion rule is arranged in the lower 1 bit. Hence, the method is effective only when a data error at the time of reproducing the multi-level data, if any, occurs in the lower 1 bit, and an erroneous judgement of the multi-level data occurs if the data error exceeds the lower 1 bit. For this reason, a multi-level data processing method has been proposed which extends the redundant data to lower k bits.
When recording (or transmitting) the multi-level data amounting to n (n≧2) bits/symbol, this proposed multi-level data processing method regards m (m≧2) symbols as 1 set, and arranges an arbitrary binary data in upper {(n−k bits)×(m symbols)}={(n−k)×m} bits of each symbol (k≧1 and n>k), and arranges a binary data which is obtained by converting (m×k−1) bits into (m×k) bits according to the predetermined conversion rule in lower {(k bits)×(m symbols)}=(m×k) bits of each symbol, so as to extend the redundant data to lower k bits. Consequently, it is possible to improve the accuracy of judging the multi-level data, even when a data transmission path has properties which generates a large number of errors. In this case, the data transmission path refers to an information recording medium such as an optical disk, a communication path and the like.
Accordingly, the conventional and proposed multi-level data processing methods employ a kind of pattern recognition technique by regarding an intersymbol interference which is generated at the time of successively recording the multi-level data as a correlation between the data. As a result, when the number of multi-levels of the multi-level data is large or the noise in the reproduced signal is large, for example, there was a problem in that the distinction of the patterns in the table becomes fuzzy to thereby cause an erroneous judgement of the multi-level data.
On the other hand, at the time of reproducing the multi-level data, a waveform equalization is carried out with respect to the reproduced signal and the intersymbol interference is eliminated, before outputting candidates of the multi-level data by judging the multi-level data using the fixed threshold value. Thereafter, the candidate having the data in accordance with the predetermined conversion rule in the lower bits of the multi-level data is selected, and the candidate having a smallest error with respect to the reproduced signal value stored in the table is output as the reproduced multi-level data. Therefore, the intersymbol interference actually remains slightly even after the waveform equalization, and there were problems in that an error may occur when outputting the candidate of the multi-level data using the fixed threshold value to judge the multi-level data, and that the final reproduced multi-level data which is output may be in error.
Accordingly, a multi-level data processing method which carries out a first multi-level data judging process and a second multi-level data judging process in parallel, and outputs a judgement result of one of the first and second multi-level data judging processes that is more appropriate, has been proposed in a Japanese Laid-Open Patent Application No. 2002-011160. FIG. 1 is a flow chart for explaining this proposed multi-level data processing method which carries out the first and second multi-level data judging processes in parallel.
In FIG. 1, a step S101 carries out the first multi-level data judging process with respect to an output signal value of a waveform equalizer circuit (not shown) which equalizes a signal reproduced from an information recording medium (not shown). More particularly, when recording the multi-level data on the information recording medium, a test data which is made up of all combinations of a plurality of (3) consecutive multi-level data is recorded on the information recording medium in addition to the multi-level data which forms the user data. When judging the multi-level data, a table which stores reproduced signal values of the test data is created. Then, the multi-level data which minimizes an error between the reproduced signal value of the multi-level data forming the user data and the reproduced signal value stored in the table is output as a judgement result of the first multi-level data judging process.
The first multi-level data judging process employs the kind of pattern recognition technique which regards the intersymbol interference generated at the time of consecutively recording the multi-level data as the correlation of the data, to judge the multi-level data. But when the number of multi-levels of the multi-level data is large or the noise in the reproduced signal is large, for example, the distinction of the patterns in the table becomes fuzzy to thereby cause an erroneous judgement of the multi-level data.
A step S103 carries out the second multi-level data judging process with respect to the output signal value of the waveform equalizer circuit. More particularly, the multi-level data forming the user data are converted from binary data into multi-level data at the time of recording onto the information recording medium. A plurality of multi-level data are treated as 1 set, and the binary data is arranged as it is in the upper bit side of each multi-level data, while the binary data is converted according to the predetermined conversion rule and arranged in the lower bit side of each multi-level data. Since the error more easily occurs in the lower bit when judging the multi-level data, the multi-level data is judged by using the fact that the data arranged in the lower bit side has been converted according to the predetermined conversion rule.
A step S105 generates judging candidates of the multi-level data of each symbol within 1 set according to the predetermined conversion rule, and outputs as a judgement result the candidate which minimizes an error between a reference value of the judging candidates and the reproduced signal value. Although a 1-bit redundant data is generated by the conversion according to the predetermined conversion rule, the accuracy of judging the multi-level data is improved.
Next, when reproducing the multi-level data, a waveform equalization is carried out with respect to the reproduced signal and the intersymbol interference is eliminated, before generating the judging candidates of the multi-level data by judging the multi-level data using the fixed threshold value. Thereafter, the judging candidate having the data in accordance with the predetermined conversion rule in the lower bits of the multi-level data is selected, and the judging candidate having a smallest error is output as the reproduced multi-level data. Therefore, the intersymbol interference actually remains slightly even after the waveform equalization, and an error may occur when generating the judging candidates of the multi-level data using the fixed threshold value to judge the multi-level data. Consequently, the final judgement result, that is, the final reproduced multi-level data which is output, may be in error. When carrying out the conversion according to the predetermined conversion rule, the data within the previous set also affects the result of the conversion, and the error may propagate for a plurality of sets.
The multi-level data forming the user data is in accordance with the predetermined conversion rule. Hence, a step S107 outputs the judgement result of the first multi-level data judging process as the reproduced multi-level data if this judgement result is in accordance with the predetermined conversion rule, because this judgement result of the first multi-level data judging process is more appropriate in this first case. On the other hand, the step S107 outputs the judgement result of the second multi-level data judging process as the reproduced multi-level data if the judgement result of the first multi-level data judging process is not in accordance with the predetermined conversion rule, because the judgement result of the second multi-level data judging process is more appropriate in this latter case.
Accordingly, it is possible to prevent an error that would be generated if the judgement result of the first multi-level data judging process is not in accordance with the predetermined conversion rule. In addition, if the judgement result of the first multi-level data judging process is in accordance with the predetermined conversion rule, it is possible to prevent an error that occurs when generating the judging candidates of the multi-level data according to the second multi-level data judging process using the fixed threshold value, and to prevent propagation of such an error.
However, the multi-level data processing method proposed in the Japanese Laid-Open Patent Application No. 2002-11160 may still output an erroneous multi-level data if the judgement result of the first multi-level data judging process is not in accordance with the predetermined conversion rule and the judgement result of the second multi-level data judging process is output as the reproduced multi-level data. In other words, if an error occurs when generating the judging candidates of the multi-level data by the second multi-level data judging process using the fixed threshold value, an error occurs in the final multi-level data that is obtained by the second multi-level data judging process as the reproduced multi-level data.